Research On Ad Hoc Network MAC Layer Protocol And Related Algorithm Improvement

Modern mobile wireless network technology,personal communication technology has developed rapidly,the traditional cellular network system has been unable to meet the development of modern communication technology,so mobile Ad Hoc network(Mobile Ad Hoc Networks,MANETs)gave birth.In the wireless network system,the MAC layer protocol controls the access performance of each node to the channel.The MAC layer protocol directly determines whether the network performance is good or bad.Because the MAC protocol is a distributed system,when the number of network nodes in the case of more,the network system can not avoid the case of packet conflict occurs.Therefore,what kind of backoff algorithm is used to reduce the occurrence of message conflict,ensure the fair access channel of each node,and improve the throughput performance of the system become an important research topic in the industry.IEEE802.11 protocol system is the main support agreement MANEYs,is also the focus of this study object,IEEE802.11 system,MAC layer using CSMA / CA(carrier monitoring multiple access / collision detection)MAC protocol.CSMA / CA uses the binary index backoff algorithm(BEB).In real applications,the BEB algorithm has poor performance and poor performance,and does not take into account factors such as retransmission limit,channel error and so on.These problem nodes have a direct impact on the access channel.And the BEB algorithm does not apply to multi-hop environments.In view of the above problems,this paper has done the following research on the backoff algorithm in IEEE802.11:Firstly,the paper studies the MAC access protocol of Ad Hoc network,and analyzes the advantages and disadvantages of these protocols.The paper mainly analyzes the defects of BEB algorithm and studies the main factors that affect the performance of BEB algorithm.The algorithm is simulated and verified by the number of retransmission times and the single hop multi-hop environment.Secondly,the existing backoff algorithm research and classification.In this paper,four kinds of backoff algorithms are simulated.It is concluded that the different backoff values should be used in the different conditions of the channel,and the state estimation of the channel is very critical.And the advantages of different backoff algorithms are used to combine the different backoff algorithms to improve the system performance.Thirdly,three kinds of dynamic adaptive backoff algorithms are proposed,and the adaptive backoff algorithm based on the transmission state change is proposed.The adaptive algorithm based on the channel node collision probability prediction is based on the transmission restriction adaptive algorithm.Based on the BEB algorithm,the logarithmic backoff algorithm is used to integrate the channel error situation that the BEB algorithm does not take into account,and the retransmission limit is incorporated into the algorithm,Retransmission times,to ensure channel access fairness and improve system saturation throughput performance.Based on the channel node collision probability prediction adaptive backoff algorithm,the channel is monitored by CSMA / CA,the busy,idle and collision time slots in the channel are counted,and the channel collision probability is calculated.According to the conflict probability,the channel is dynamically adapted to different states To ensure the improvement of system performance.The adaptive backoff algorithm based on transmission restriction combines the linear backoff algorithm and the exponential backoff algorithm.The algorithm is designed to enable the nodes to access the channels as much as possible under the three retransmission times and make the CW window values of the nodes as inconsistent as possible.In this case,when the channel competition is intense,the algorithm uses other nodes to avoid the time slot,and consciously makes the node with smaller window value lower access channel,which can greatly improve the channel saturation throughput,but based on transmission limit adaptive The backoff algorithm sacrifices fairness to a certain extent.Finally,this paper compares the performance of the three algorithms based on the transmission constrained adaptive algorithm based on the adaptive prediction algorithm based on the transmission state change and the adaptive prediction algorithm based on the channel node collision probability prediction.The experimental results show that the three algorithms can improve the performance of the system and the performance of the fairness coefficient.The results show that the three algorithms can improve the performance of the system.